Compression guidelines

Compression gives you the flexibility to configure on a per-point basis, with the option of archiving relevant information. Compression impacts performance, bandwidth, and data access. Compression not only saves storage space, it also helps you to store only meaningful data. Data Archive stores the actual values received from the source, not interpolations, averages, or approximations. This dramatically improves performance for users and does not cause loss of significant data.

You have complete control over the amount of compression used, from the most compression (lossy) to the least compression (lossless). For example:

• Turn compression on for noisy signals.

• Turn compression on and set the compression deviation (CompDev) attribute to zero. With this setting, successive identical values (or values aligning perfectly) are not archived. This is more efficient than turning compression off.

• Turn compression off for manually entered and totalized data, and for points where each event is significant and not merely representative of an underlying flow (such as lab measurements). When compression is turned off, all exceptions are recorded.

A Data Archive installation with default compression values is appropriate for most cases.

Setting compression requires you to apply your process knowledge about the nature of the signal. One compression-deviation specification does not work for all measurements. Consider sensor type, instrument accuracy, and so on. Fortunately, there are broad categories of measurements in a process plant. Similar flow meters, pressure gauges, and thermocouples have the same degree of repeatability and reproducibility in their measurements.